1. Field Of The Invention
This invention relates to subsurface control valves used in closing off a well annulus in situations where necessary such as a storm on an offshore location, and more particularly, to a subsurface control valve having a substantially unobstructed flow passageway therethrough and having a valve element in a normally open position as the tool string is lowered into the well.
2. Description Of The Prior Art
A subsurface control valve using a sliding inner sleeve valve element within an outer sleeve is disclosed in U.S. Pat. No. 4,372,388 to Skinner. In this valve, openings in the inner sleeve are aligned with openings in the outer sleeve for flow therethrough. Fluid may flow down a central opening through the tool string, pass through these transverse openings into an annulus around the other sleeve and thus downward to the lower tool string portions. Such an arrangement results in pressure drop through the valve. The present invention has a totally unobstructed flow passageway when the valve is in an open position, and thus pressure drop therethrough is virtually eliminated.
The valve of Skinner is attached to a stinger assembly and is in a normally open position as the valve is run into the well. To close the valve, rotation of the stinger assembly is required, after which it may be removed from the well bore. To reattach and reopen the valve, the stinger assembly is run back into the well and rotatingly engaged with the valve assembly by rotating in the direction opposite to that required for disengagement. The subsurface control valve in the present invention is maintained in an open position by tension due to the weight of the tool string elements below it, and the valve is closed by simple movement of the tool string when the tension on it is released.
Use of a pressure balancing piston in a packer is disclosed at page 3477 of Halliburton Services Catalog No. 40. Typical examples of other subsurface control apparatus are disclosed in U.S. Pat. No. 3,356,140 to Young and U.S. Pat. No. 3,570,595 to Berryman. None of these references discloses a normally open subsurface control valve having a fully unobstructed flow passage therethrough which is held in an open position by the weight of the tool string elements below the valve, or which utilizes a retrieving mechanism such as in the present invention.